Editing 70 mm film (section)

===Todd-AO===
[[File:65 mm film (5-70).svg|thumb|right|upright=1.42|Todd-AO / Panavision (5-perf) 65 mm negative frame dimensions; the ''Ultra Panavision'' 1.25× anamorphic process is represented by the distorted circle.]]
{{main|Todd-AO process}}
Producer [[Mike Todd]] had been one of the founders of [[Cinerama]], a wide-screen movie process that was launched in 1952. Cinerama employed three 35&nbsp;mm film projectors running in synchronism to project a wide (2.6:1) image onto a deeply curved screen. Although the results were impressive, the system was expensive, cumbersome and had some serious shortcomings due to the need to match up three separate projected images. Todd left the company to develop a system of his own which, he hoped, would be as impressive as Cinerama, yet be simpler and cheaper and avoid the problems associated with three-strip projection; in his own words, he wanted "Cinerama out of one hole".

In collaboration with the [[American Optical Company]], Todd developed a system which was to be called "[[Todd-AO]]". This uses a single 70&nbsp;mm wide film and was introduced with the film ''[[Oklahoma! (film)|Oklahoma!]]'' in October 1955. The 70&nbsp;mm film is perforated at the same pitch (0.187 inch, 4.75&nbsp;mm) as standard 35&nbsp;mm film. With a five-perforation pull-down, the Todd-AO system provides a frame dimension of 1.912 inch (48.56&nbsp;mm) by 0.87 inch (22.09&nbsp;mm) giving an aspect ratio of 2.2:1.

The original version of Todd-AO used a frame rate of 30 per second, 25% faster than the 24 frames per second that was (and is) the standard; this was changed after the second film – ''[[Around the World in 80 Days (1956 film)|Around the World in 80 Days]]'' - because of the need to produce (24 frame/sec) 35&nbsp;mm reduction prints from the Todd-AO 65&nbsp;mm negative. The Todd-AO format was originally intended to use a deeply curved Cinerama-type screen but this failed to survive beyond the first few films.<ref>"In the Splendour of 70&nbsp;mm Part 1" Grant Lobban, Journal of the BKSTS Vol68 No.12 December 1986</ref> However, in the 1960s and 70s, such films as ''[[The Sound of Music (film)|The Sound of Music]]'' (which had been filmed in Todd-AO) and ''[[Patton (film)|Patton]]'' (which had been filmed in a copycat process known as Dimension 150) were shown in some Cinerama cinemas, which allowed for deeply curved screens.<ref>{{cite web|url=http://cinematreasures.org/theaters/4784|title=Atlanta Theatre|work=Cinema Treasures|access-date=1 December 2015}}</ref>

Todd-AO adopted a similar multi-channel magnetic sound system to the one developed for [[Cinemascope]] two years earlier, recorded on "stripes" of magnetic oxide deposited on the film. However Todd-AO has six channels instead of the four of Cinemascope and due to the wider stripes and faster film speed provides superior audio quality. Five of these six channels are fed to five speakers spaced behind the screen, and the sixth is fed to surround speakers around the walls of the auditorium.